A free app for Android, by Japan Gor.

GJAM is a free, safe, and simple app for Android that allows you to copy, move, rename, delete, or share your files between internal and external storage. With it, you can manage your phone and storage in an organized way, either by folders or by files. You can even browse your files by categories. It’s all very easy to use and can be done without the need to root your device.

You can also transfer files and folders between devices or to a cloud storage account. The app supports SD cards, Micro SD cards, and internal storage.